The long term goal of this study is to identify essential components in the IRBP promoter required for full protein expression. These components include cis-elements, a basal promoter, small effector molecules and trans factors. Previous work has identified a short (less than 70 bp) essential IRBP promoter region, demonstrated that chick retina primary cell cultures provide a suitable in vitro assay system for IRBP promoter activity, identified a specific trans factor and devised a model of the IRBP promoter. The primary strategy is to exploit the promoter activity measurements in the retina cell culture of mutated IRBP promoters. The specific aims are: (1) to test whether the two cis-activators and basal promoter exist as proposed; (2) to test whether the putative retinoic acid receptor/estrogen receptor element shows responsiveness to these effector molecules in IRBP promoter activation; and (3) to test whether the first two proposed trans factors exist and to identify, clone or purify the above mentioned trans factor for the -55 to -50 cis-element. The experiments will either prove the proposed model correct or lead to appropriate revisions. The research will be significant in understanding of the basics of IRBP gene expression, clarifying of transcriptional issues and obstacles for gene therapy in the retina, creating practical tools for future photoreceptor-specific gene therapy, and understanding the coordination of photoreceptor-specific gene transcription.